2012 h1 jc2 prelim - core

Civics Group

Index Number

Name (use BLOCK LETTERS)

ST. ANDREW’S JUNIOR COLLEGE2012 Preliminary Examination

H1 BIOLOGY 8875/2

Paper 2: Core

Friday 14 September 2012 2 hours

Additional Materials: Answer PaperCover Sheet for Section B

READ THESE INSTRUCTIONS FIRST

Write your name, civics group and index number on all the work you hand in.Write in dark blue or black pen on both sides of the paper.You may use a soft pencil for any diagram, graph or rough working.Do not use staples, paper clips, highlighters, glue or correction fluid.

Section AAnswer all the questions.

Section BCompulsory question to be answered on writing paper provided.

At the end of the examination, fasten all your work securely together.The number of marks is given in brackets [ ] at the end of each question or part question.

For Examiner’s Use

Section A

1 /12½

2 /9

3 /10

4 /8½

5/6 /20

Total /60

This document consists of 12 printed pages.[Turn over

H1

2

Section A

Answer all questions.

QUESTION 1

Figure 1.1 is a diagram of an animal cell as seen using a transmission electron microscope.

Figure 1.1

(a) Name the structures of the cell labelled A, B, C and D. [2]

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(b) Structures C and E are examples of the same organelle. Suggest 2 reasons why E looks so different to C.

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[1]

SAJC / H1 Biology 8875/2 JC2 Preliminary Examinations 2012

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(c) Proteins are produced by the structure labeled F. Some of these proteins may be extracellular proteins that are released from the cell.

Outline the sequence of events following the production of extracellular proteins that leads to their release from the cell.

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(d) The division of stem cells by mitosis produces genetically identical cells.

(i) Explain what is meant by the term pluripotency.

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(ii) Explain the normal functions of blood stem cells (found in the bone marrow) in a living organism.

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(iii) Suggest how a blood stem cell could differentiate into its specialized cells.

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QUESTION 2

(a) Explain the natural function of restriction endonucleases

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Figure 2.1 shows the structure of a functional insulin molecule. It is composed of two polypeptide chains: an A chain of 21 amino acids and a B chain of 30 amino acids. These two chains are held together by two disulfide bonds formed between two amino acid residues.

Figure 2.1

Currently, the production of recombinant insulin involves artificially synthesising the genes for the A chain and the B chain and then inserting each into 2 separate plasmids such that two recombinant plasmids are constructed (Figure 2.2), one carrying the gene for the A chain and one the gene for the B chain.

The A chains and B chains are synthesised separately in two different batches of E.coli. The two protein chains are then extracted and purified. Finally, the A and B protein chains are mixed under special conditions allowing disulphide bonds to form in vitro.

Figure 2.2

(b) State the function of the β-galactosidase gene in the plasmids.

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gene for chain A

gene for chain B

gene for β-galactosidase

gene for β-galactosidase

lac promoter lac promoter

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[1]


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(c) Explain the addition of the lac promoter in both vectors used for the insertion of genes for chain A and B.

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(d) Explain how the cells must be first treated in order for transformation to occur.

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(e) Suggest how the above introduction of recombinant DNA molecules into host cells is similar to mutations.

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(f) State two advantages of treating diabetics with human insulin produced by genetic engineering.

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[1]

(g) The recombinant chain A and B protein produced as described above is identical to naturally occuring human insulin chains A and B.


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However, the synthetic gene inserted into the plasmid may possess a different nucleotide sequence to the actual human gene. Give reasons why this is so.

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QUESTION 3

Many varieties of rice, Oryza sativa, die quickly when totally submerged by flood water during the monsoon season.

Figure 3.1 Source : Wikipedia

In 2006, a gene, Sub1A, on rice chromosome 9 was found to be involved in tolerance of prolonged submergence.

An allele, Sub1A-1, was found only in submergence-tolerant rice. Varities that are submergence-intolerant either have a second allele, Sub1A-2, or lack the gene altogether.

(a) Sub1A-1 codes for a protein that controls the transcription of the gene for alcohol dehydrogenase. This gene is activated when the plant is in anaerobic conditions.

Explain the importance to submerged rice plants of producing alcohol dehydrogenase.

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(b) Alleles Sub1A-1 and Sub1A-2 differ by one nucleotide. The amino acid, serine, in the protein produced by submergence-tolerant plants is replaced by proline in submergence-intolerant plants.

Suggest why the protein produced by submergence-intolerant plants in inactive.

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A variety of submergence-intolerant rice, which lacked the gene Sub1A, was genetically engineered to express Sub1A-1.

Typically, submergence-intolerant plants respond to submerged conditions by elongating rapidly.

The mean heights of three types of rice plants were compared before and after 10 days of submergence in water. The types of rice plants were:

submergence-intolerant plants, I transgenic submergence-intolerant plants expressing Sub1A-1, I+

submergence-tolerant plants, T.

The results are shown in Figure 3.2


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Figure 3.2


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(c) With reference to Figure 3.2,

(i) Describe the effect of submergence on the three types of rice plants.

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(ii) Suggest a reason why the response shown by the submergence-intolerant plants, I, may lead to their death.

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(d) The allele Sub1A-1 could be introduced into high-yielding variety of submergence-intolerant rice either by genetic engineering or by selective breeding.

State two advantages of using genetic engineering, rather than selective breeding, to introduce the allele.

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QUESTION 4

Scientists have been studying finches on an island in the Galapagos for over thirty years.

Before 1982, the only type of ground finch living on the island was the medium ground finch, Geospiza fortis.

In 1982, the large ground finch, Geospiza magnirostris settled on the island. The large ground finch is almost twice the size of the medium ground finch.

Figure 4.1

The key food for both species is the large seed from the plant Tribulus cistoides. Both species use their beaks to crack open the seeds.

During the period of the study, there have been two major droughts in 1977 and 2003. Some of the observations made by the scientists are listed below :

The drought in 1977 wiped out mainly plant species producing small seeds, leaving Tribulus cistoides plants that produced large seeds with hard coats.

Following the 1977 drought, the population of the medium ground finch was greatly reduced and the average beak size had increased in both length and depth by approximately 4%.

The 2003 drought greatly reduced seed production by all plants including Tribulus cistoides.

Measurements were made of the beak mean lengths and mean beak depths of the medium ground finch population in both 2002 and 2005. These are shown in Table 4.1

2002 2005 % decreaseMean beak length /mm 11.2 10.6

Mean beak depth /mm 9.4 8.6

Table 4.1

(a) Calculate the percentage decreases in the mean length and mean depth of the beaks of the medium ground finch population between 2002 and 2005. Write your answers in Table 4.1. [1]


1 – Geospiza magnirostris2 – Geospize fortis

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(b) State the two main selection pressures acting on the medium ground finch population following the 2003 drought.

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(c) State how selection pressure on the medium ground finch population was different following the 1977 drought.

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(d) Explain the mechanism that has produced this change in mean beak size in the medium ground finch population between 2002 and 2005.

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[4]

(e) It was suggested from the data in Table 4.1 that stabilizing selection was taking place in the medium ground finch population.

State whether you agree with this statement and explain your answer.

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Section B

Answer the question.

Write your answers on the separate answer paper provided.Your answers should be illustrated by large, clearly labelled diagrams, where

appropriate.Your answers must be in continuous prose, where appropriate.

Your answers must be set out in sections (a), (b) etc., as indicated in the question.

5 (a) Distinguish between chromosomal and gene mutation. [5]

(b) With reference to specific examples, explain the significance of genetic engineering in improving the quality and yield of crop plants and animals in solving the demand for food in the world.

[8]

(c) Describe how the structure of the membrane affects the movement of substances into and out of a cell.

[7]

6 (a) Compare the structure of collagen and cellulose. [5]

(b) Describe how information on mature mRNA is used to synthesise polypeptides in eukaryotes.

[8]

(c) Describe the source of genetic variation in a population of sexually reproducing organisms.

[7]

- END OF PAPER -


2012 h1 jc2 prelim - core

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